Determination of the age of a basic igneous intrusion by the potassium-argon method

Abstract

POTASSIUM-ARGON age determinations have been carried out mainly on minerals with a high potassium content, particularly micas and potassium feldspars, found in intermediate to acid igneous rocks, but little work has been done on minerals with a low content of potassium, such as occur in basic igneous rocks. However, Hart et al.1 have shown recently that it is possible to obtain reliable ages using hornblende and pyroxene. I decided to investigate the relative argon retention properties of pyroxene, plagioclase and sanidine in two specimens from a Tasmanian dolerite body, and in so doing hoped to determine the time of intrusion of the dolerite. The presence of chilled margins to these dolerite intrusions also suggested the possibility of carrying out potassium-argon dating on a whole rock sample from such a contact. Show more